LES RISQUES NATURELS LIES À LA PLUIE ET À LA SÉCHERESSE : ELABORATION DE CARTES DES PLUIES EXTRÊMES ET DES RISQUES D’INCENDIES DE FORÊT DANS UNE RÉGION MÉDITERRANEENNE : LA TOSCANE (ITALIE)
PIERRE CARREGA
ABSTRACT. – The Natural Risks Connected to Rainfall and Drought: Drawing Maps of Extreme Rainfalls and Risks of Forest Fires within a Mediterranean Region: Toscana (Italy). A detailed analysis of natural risks shows that the traditional distinction between “probability of occurrence” and site “vulnerability” is frequently insufficient to describe and understand natural catastrophes. An intermediate variable, called “susceptibility" (risk potential) is needed to link probability of occurrence to vulnerability. Risk potential is the likelihood that a natural risk (probability of occurrence) will create a phenomenon with variable consequences (vulnerability).The distinction described above refines the usual risk maps generated from automatic maps softwares or Geographic Information Systems (GIS). These tools are essential for both scientists and decision-makers because they provide a spatial view of the different aspects associated with natural risks: return period of dangerous phenomena (extreme rainfall events, forest fire initiation...), the susceptibility that the phenomenon will take on dangerous proportions (fire propagation in highly inflammable vegetation, runoff rates accelerated due to steep slopes and geological substrate...), catastrophic repercussions linked to site vulnerability (flash floods carrying off cars and causing victims, houses destroyed by forest fires...).